The present invention relates to an electric gas-lighter which may be applied, for example, to the cooking range of a gas cooker.
Cooking ranges are known which are fitted with built-in electric gas-lighters operated manually to produce sparks and light gas flames on the range.
One type of cooking range with an electric gas-lighter (FIG. 1) comprises metal gas burners 2, each provided with a respective electrode 3 located to the side of the burner 2 and insulated electrically with respect to the grounded metal surface 4 supporting the burners.
When operated, the electric gas-lighter produces a spark between each electrode 3 and the respective burner 2 to light the flame of the burner supplied with gas.
FIG. 1 shows a complete circuit diagram of one known type of gas-lighter.
In addition to electrodes 3, the gas-lighter comprises a first and a second input terminal 7, 8 connectable to a supply line, e.g. an alternating mains line (not shown), by closing a switch (not shown); and an electric-discharge generating circuit 5 interposed between input terminals 7, 8 and electrodes 3, for producing the sparks on electrodes 3.
Circuit 5 comprises a resistor 9 having a first terminal connected to input terminal 7, and a second terminal connected to the anode of a rectifying diode 10, the cathode of which is connected to a first node 11.
Circuit 5 also comprises a capacitor 12 having a first terminal connected to node 11, and a second terminal connected to a node 13 in turn connected to second input terminal 8.
Circuit 5 also comprises a voltage discharge device 15 having a first terminal connected to node 11, and a second terminal connected to a first terminal 16a of a primary winding 16 of a transformer 17. The primary winding of transformer 17 has a second input terminal 16b connected to node 13, and transformer 17 also comprises two identical secondary windings 18, each having far more turns than primary winding 16.
The terminals of each secondary winding 18 are connected to respective electrodes 3.
The gas-lighter operates as follows.
When the switch (not shown) is closed to connect the gas-lighter circuit to the alternating supply line, the alternating mains voltage is rectified by diode 10 and a rectified voltage is applied to charge capacitor 12. When the voltage at the capacitor terminals reaches a threshold value VTH equal to the ignition threshold value of discharger 15, transformer 17 and capacitor 12 are connected, and capacitor 12 discharges via primary winding 16. A discharge current ISC of extremely high intensity (e.g. a 150-280 A peak) is thus generated and flows through primary winding 16, at the terminals of which a discharge voltage V1 (e.g. of 400 V) is generated during the discharge transient (lasting a few microseconds). Discharge voltage V1 induces, at the terminals of secondary windings 18, a voltage V2 much higher than V1 (e.g. 28 kV) and which is applied to electrodes 3. For each secondary winding 18, voltage V2 is sufficient to produce sparks between each electrode 3 and metal burner 2, which is grounded.
Gas-lighters of the above type have the drawback of generating, at the output (i.e. towards the supply mains) and during the discharge transient, severe electromagnetic noise above the limits laid down by European standards (EN55014 and following).
One proposed solution to the problem is to fit the gas-lighter with an electronic filter to reduce the electromagnetic noise at the output and so obtain a low-noise gas-lighter as shown in FIG. 2. In addition to the components described above (indicated using the same reference numbers), a low-noise gas-lighter comprises an electronic filter 20 interposed between terminals 7, 8 and a circuit 5a equivalent to circuit 5 but having no resistor 9.
Filter 20 comprises a first decoupling resistor 25a having a first terminal connected to terminal 7 and a second terminal connected to a node 22 communicating with the anode of diode 10 and with a first terminal of a capacitor 21a having a second terminal connected to a reference potential (ground). Filter 20 also comprises a second decoupling resistor 25b having a first terminal connected to terminal 8 and a second terminal connected to a node 23 communicating with node 13 and with a first terminal of a capacitor 21b having a second terminal connected to the reference potential (ground).
Capacitors 21a and 21b are thus located between respective nodes 22 and 23 and a common node 24 which is the ground.
Filter 20 defines a preferential path by which to discharge the electromagnetic energy produced during the discharge transient of capacitor 12. More specifically, this energy is conveyed by capacitors 21a and 21b directly towards ground 24 to reduce the electromagnetic emissions emitted by the circuit towards the supply mains.
Though filter 20 indeed provides for reducing the noise level generated during operation to well below the prescribed limit, gas-lighters fitted with filters 20 are not without further drawbacks.
Though minimum per gas-lighter, the expense of providing the filter with two capacitors is far from negligible on a mass-production scale, as in the household appliance industry.
It is an object of the present invention to provide an electric gas-lighter which is highly straightforward, and which at the same time provides for eliminating the drawbacks associated with gas-lighters of the type described above.
According to the present invention, there is disclosed an electric gas lighter having a discharge generating circuit comprising input terminals connectable to a supply source and at least one output terminal for generating sparks. The gas lighter also comprises a filter for filtering electromagnetic noise. The filter consists essentially of a single capacitor having a first terminal communicating with a reference potential and a second terminal communicating with one of the input terminals through a first resistor.